Long, short, bouncy, sleek -- for most women, hair is far more than a bundle of fiber. It's an expression of style and personality. Research also suggests hair and self-image are closely intertwined. If an occasional "bad hair day" can make a woman feel bad, hair loss can be a distressing sight to face every morning in the mirror.

Hair loss common in women, too

The idea that thinning hair is a guy problem is simply wrong. Forty percent of people who experience temporary or long term hair loss are women. Some have hair that is thinning all over, while others see the center part gradually widen. Still others develop distinct baldness at the crown of the head. Unlike men, women rarely develop a receding front hairline.

How hair grows

The average scalp has 100,000 hairs. Each follicle produces a single hair that grows at a rate of half an inch per month. After growing for two to six years, hair rests awhile before falling out. It's soon replaced with a new hair, and the cycle begins again. At any given time, 85% of hair is growing, and the remainder is resting.

How much hair loss is normal?

Because resting hairs regularly fall out, most people shed about 50-100 strands every day. You'll typically find a few in your hairbrush or on your clothes. Abnormal hair loss can happen in several ways. You may notice dramatic clumps falling out when you shampoo or style. Or your hair may thin slowly over time. If you're concerned about changes in your hair, check with your doctor.

Finding the roots of hair loss

Hair loss in women can be triggered by about 30 different medical conditions, as well as several lifestyle factors. Sometimes no specific cause can be found. As a starting point, hair loss experts recommend testing for thyroid problems and hormone imbalances. In many cases, hair will grow back once the cause is addressed.

Measuring women's hair loss

The Savin scale is a common measure that ranges from normal hair density to a bald crown (very rare). It's helpful in documenting female pattern baldness, which affects many women. Experts think genetics and aging play a role in androgenic alopecia, along with the hormonal changes of menopause. Hair may become thin all over, with the greatest loss along the center of the scalp. A receding hairline is very rare in women.

Hair loss trigger: Thyroid problems

The thyroid is a butterfly-shaped gland at the front of the neck. It produces hormones that regulate many processes throughout the body. If the gland makes too much or too little thyroid hormone, the hair growth cycle may falter. But hair loss is rarely the only sign of a thyroid problem. Other symptoms include weight gain or loss, sensitivity to cold or heat, and changes in heart rate.

Hair loss trigger: PCOS

Women with polycystic ovary syndrome (PCOS) have a chronic hormonal imbalance. The body makes higher levels of androgens than expected. This often causes extra hair to sprout on the face and body, while hair on the scalp grows thinner. PCOS can also lead to ovulation problems, acne, and weight gain. But sometimes thinning hair is the only obvious sign.

Hair loss trigger: Alopecia areata

Alopecia areata causes hair to fall out in startling patches. The culprit is the body's own immune system, which mistakenly attacks healthy hair follicles. In most cases, the damage is not permanent. The missing patches usually grow back in six months to a year. In rare cases, people may lose all of the hair on their scalp and body.

Hair loss trigger: Ringworm

When ringworm affects the scalp, the fungus triggers a distinct pattern of hair loss -- itchy, round bald patches. Bald areas can appear scaly and red. Ringworm of the scalp is treated with antifungal medication. The fungus is easily spread by direct contact, so family members should be checked for symptoms, too.

Hair loss trigger: Childbirth

Some women may notice their hair seems fuller during pregnancy. That's thanks to high levels of hormones that keep resting hairs from falling out as they normally would. But it doesn't last forever. After childbirth, when hormone levels return to normal, those strands fall out quickly. This can mean a surprising amount of hair loss at one time. It may take up to two years for hair to return to normal.

Hair loss trigger: The pill

A little known side effect of birth control pills is the potential for hair loss. The hormones that suppress ovulation can cause hair to thin in some women, particularly those with a family history of hair loss. Sometimes hair loss begins when you stop taking the pill. Other drugs linked to hair loss include blood thinners and medicines that treat high blood pressure, heart disease, arthritis, and depression.

Hair loss trigger: Crash diets

You may lose more than weight with a crash diet. People may notice hair loss 3-6 months after losing more than 15 pounds, but hair should regrow on its own with a healthy diet. Be prepared to shed some locks if your diet is very low in protein or too high in vitamin A.

Hair loss trigger: Tight hairstyles

It's no myth: Wearing cornrows or tight ponytails can irritate the scalp and cause hair to fall out. The same is true of using tight rollers. Let your hair down, and it should grow back normally. Be aware that long-term use of these styles can cause scarring of the scalp and permanent hair loss.

Hair loss trigger: Cancer treatment

Hair loss is an infamous side effect of two cancer treatments: chemo and radiation therapy. In their quest to kill cancer cells, both treatments can harm hair follicles, triggering dramatic hair loss. But the damage is almost always short-lived. Once the therapy is finished, hair usually grows back.

Hair loss trigger: Extreme stress

Extreme physical or emotional stress can cause a sudden shedding of one-half to three-quarters of the hair on your head. Examples include:

*Serious illness or major surgery

*Trauma involving blood loss

*Severe emotional trauma

The shedding may last six to eight months.

Treating hair loss: Medicine

Minoxidil (Rogaine) is approved by the FDA for female pattern hair loss. It can slow or stop hair loss in most women and may help hair grow back in up to a quarter of those who use it. The benefits are lost when you stop using it. For women with alopecia areata, corticosteroids can help regrow hair. And if you have an underlying medical problem or a nutritional deficiency, hair usually grows back on its own once that condition is under control.

Treating hair loss: Laser devices

Devices that emit low-energy laser light may stimulate hair growth to help fight thinning hair. They're available in some clinics and as hand-held devices to use at home. At least one device has gained FDA approval for both men and women, based on a small study that showed effectiveness in at least some of those who tested it. It took 2-4 months to see the results. The FDA does not require the same rigorous testing for devices as for medicines. The long-term safety and effectiveness are unknown.

Hair transplants in women

This procedure involves moving hair to thinning scalp areas from donor sites. The trouble is, female pattern baldness causes thin hair all over, so good donor sites may be limited. The exceptions are women with male pattern baldness or hair loss caused by scarring.

Hair-loss products and devices

A quick Internet search will turn up dozens of products intended to stop hair loss or regrow hair. Unfortunately, there's no way to know whether before and after pictures have been doctored. To evaluate a hair-loss treatment, you can check with:

*A dermatologist

*The FDA medical devices division

*The Federal Trade Commission (FTC)

Coping with thinning hair

Ask your stylist for tips -- a short cut, a different part, maybe a gentle body wave. A styling product for thin hair may help hide hair loss. You apply it to the root area and gently blow dry to build volume. (Let hair air dry partially before using a blow dryer.) Special cosmetics can camouflage visible areas of scalp. And keratin fiber hair cosmetics may be worth a try. They're sprinkled over the thinning patch, where their static charge makes hair appear thicker.

Coping with significant hair loss

Adjusting to permanent hair loss is challenging for most women. If thin areas are very obvious, consider a weave, a hairpiece, a scarf, or a hat to cover bald spots. Good quality wigs are more comfortable than ever -- and they rarely have bad hair days. If hair loss interferes with your job or social life or makes you reluctant to leave the house, think about talking with a counselor.